Detailed notes on nervous tissue for Class 9 from the NCERT Exploration textbook (Chapter 3: Tissues in Action). Topics covered: what is nervous tissue, the neuron as the basic unit, structure of a neuron — cell body, dendrites, axon, axon terminals — and how a nerve impulse travels from stimulus to response. Includes a diagram label guide for Fig. 3.14 and quick revision. Aligned with CBSE syllabus 2026–27.
In Class 9 Chapter 3 (Tissues in Action), nervous tissue is the fourth and final type of animal tissue you study — after epithelial tissue, connective tissue, and muscular tissue. Nervous tissue forms the body's control and coordination network. It makes up the brain, spinal cord, and all the nerves that run throughout the body.
Definition
Nervous tissue is an animal tissue that is highly specialised for receiving, processing, and transmitting information in the form of electrical signals called nerve impulses. Its basic structural and functional unit is the neuron (nerve cell). Nervous tissue is found in the brain, spinal cord, and nerves — together forming the nervous system that coordinates all activities of the body.
The brain acts as the central control centre of the body. It receives information from the environment and from within the body, processes it, and sends out appropriate responses via nerves. This is possible because nervous tissue is made of neurons — cells uniquely built to carry messages at great speed over long distances.
2. Why is Nervous Tissue Important?
Q. Why do we need nervous tissue? Give examples.
Without nervous tissue, the body would have no way to detect the outside world or coordinate its own activities. Consider these everyday examples:
Pulling your hand away from a hot surface — sensory neurons carry a pain signal from your skin to the spinal cord; motor neurons carry the response signal back to your arm muscles, which contract to withdraw your hand. All of this happens in a fraction of a second.
Remembering a song — the brain stores and retrieves memories through complex networks of neurons. Memory, thought, and learning are entirely dependent on nervous tissue.
Heart beating faster during exercise — when muscles demand more oxygen, the brain sends signals via nerves to increase the heart rate. The cardiac muscle responds to these nerve signals by beating faster.
Control and Coordination
Control and coordination in animals is entirely dependent on nervous tissue. Every voluntary movement you make — walking, writing, speaking — is initiated and controlled by the nervous system. Every involuntary process — breathing, digestion, heartbeat — is regulated by it too.
3. What is a Neuron?
Q. What is a neuron and why is it called the basic unit of nervous tissue?
A neuron (also called a nerve cell) is the basic structural and functional unit of nervous tissue. Just as the cell is the basic unit of all living things, the neuron is the basic unit of the nervous system. Nervous tissue is composed of billions of neurons working together.
Definition: Neuron
A neuron is a highly specialised cell that is adapted to receive stimuli (from the environment or from other neurons), process the information, and transmit nerve impulses to other neurons, muscles, or glands. Neurons are the longest cells in the human body — a single motor neuron in your leg can be over a metre long.
Neurons are classified by their role: sensory neurons carry information from sense organs (eyes, skin, ears) towards the brain or spinal cord; motor neurons carry commands from the brain or spinal cord out to muscles and glands; and interneurons connect sensory and motor neurons within the brain and spinal cord.
4. Structure of a Neuron
Q. Describe the structure of a neuron with a labelled diagram.
A neuron has three main parts: the cell body, dendrites, and an axon ending in axon terminals. This structure is precisely suited to the neuron's job of receiving and transmitting nerve impulses.
Fig. 3.14 (NCERT Exploration): Structure of a neuron — showing cell body (cyton) with nucleus, branched dendrites, long axon with myelin sheath, and axon terminals (synaptic knobs).
4.1 Cell Body (Cyton)
The cell body (also called the cyton or soma) is the main metabolic centre of the neuron.
It contains the nucleus, which controls all cell activities, along with the usual cell organelles — mitochondria, endoplasmic reticulum, and Golgi apparatus.
The cell body also contains Nissl bodies — clumps of rough endoplasmic reticulum that produce proteins needed for the neuron's activity and repair.
The cell body processes the incoming signals received by the dendrites and decides whether to generate and pass on a nerve impulse.
4.2 Dendrites
Dendrites are short, highly branched extensions that arise from the cell body.
Their name comes from the Greek word for tree — their branching shape resembles the branches of a tree.
Dendrites are the input zone of the neuron: they receive nerve impulses (signals) from other neurons and carry them towards the cell body.
The more dendrites a neuron has, the more connections it can receive — neurons in the brain can have thousands of dendritic branches.
4.3 Axon
The axon is a single, long fibre that arises from a cone-shaped region of the cell body called the axon hillock.
The axon carries the nerve impulse away from the cell body towards the next neuron, muscle, or gland.
Many axons are covered by a fatty white insulating sheath called the myelin sheath, produced by specialised cells called Schwann cells. The myelin sheath speeds up impulse transmission and protects the axon.
Axons can be very long — motor neurons that control the muscles of the foot have axons that travel from the spinal cord all the way to the foot, a distance of over a metre.
4.4 Axon Terminals
At its far end, the axon divides into several fine branches, each ending in a small swelling called the axon terminal (or synaptic knob).
Axon terminals are the output zone of the neuron: they transmit the nerve impulse to the next cell (another neuron, a muscle fibre, or a gland cell).
The junction between an axon terminal and the next cell is called a synapse. At the synapse, the electrical impulse triggers the release of chemical messengers called neurotransmitters, which carry the signal across the tiny gap to the next cell.
Remember — Direction of Signal Flow in a Neuron
Dendrites → Cell Body → Axon → Axon Terminals
Signal always flows in ONE direction within a single neuron: received by dendrites, processed by cell body, transmitted along axon, passed on at axon terminals. This one-way flow ensures orderly and precise communication in the nervous system.
5. How Does a Message Travel?
Q. How does a nerve impulse travel through the nervous system?
A nerve impulse is an electrical signal that travels along the neuron membrane. The journey of a message through the nervous system can be understood in three steps:
3-Step Flow of a Nerve Impulse
Receive — Dendrites pick up the stimulus (e.g., heat from a flame, pressure on the skin) and generate an electrical signal.
Process — The signal travels to the cell body, which integrates all incoming information and, if the signal is strong enough, generates a nerve impulse.
Transmit — The impulse races along the axon to the axon terminals, where neurotransmitters are released into the synapse to pass the message to the next neuron, muscle, or gland.
This three-step process repeats from one neuron to the next in a chain, carrying the message from its origin (e.g., a fingertip touching a hot surface) all the way to the response (muscles contracting to pull the hand away). In muscular tissue, the final motor neuron signals the muscle fibre to contract.
6. Role of Nervous Tissue in the Musculoskeletal System
Q. Can muscles work without nervous tissue?
No — muscular tissue cannot act without signals from nervous tissue. This interdependence is one of the most important ideas in the study of animal tissues.
Voluntary movement — when you decide to move your arm, the brain sends a motor nerve impulse along a motor neuron. The axon terminal of the motor neuron releases neurotransmitters at the neuromuscular junction (where nerve meets skeletal muscle), triggering the muscle fibre to contract. Without this nerve signal, the muscle stays still no matter how healthy it is.
Involuntary regulation — the brain continuously monitors and adjusts the heart rate. During exercise, when the body needs more oxygen, the brain sends increased impulses via the autonomic nervous system to the cardiac muscle, causing it to beat faster. The bones and tendons provide the mechanical leverage — but the instruction always originates in nervous tissue.
Tissues Working Together
Movement in the animal body is a team effort: nervous tissue (brain + neurons) issues the command → muscular tissue (skeletal muscle) contracts → connective tissue (tendon) transmits the force → connective tissue (bone) moves at the joint. All four tissue types must function together for even a simple action like picking up a pen.
7. Diagram Label Guide — Fig. 3.14 (Neuron)
Q. What are the parts to label in the diagram of a neuron (Fig. 3.14 NCERT Exploration)?
Fig. 3.14 (NCERT Exploration): A typical motor neuron. Learn the position of each labelled part for diagram-based exam questions.
The typical neuron diagram in NCERT Exploration (Fig. 3.14) shows the following parts to identify and label:
Part
Position in Diagram
Function
Cell Body (Cyton)
Central rounded region with a large nucleus visible inside
Contains nucleus; metabolic and processing centre
Nucleus
Inside the cell body — large, prominent
Controls all cell activities
Dendrites
Short, branched extensions radiating from the cell body
Receive incoming nerve impulses
Axon
Single long fibre extending from the cell body
Carries impulse away from cell body
Myelin Sheath
Segmented white covering around the axon
Insulates axon; speeds up impulse conduction
Axon Terminals
Branched endings at the far end of the axon (small swellings)
Transmit impulse to next cell via synapse
8. Quick Revision — 4 Key Points
Nervous tissue forms the brain, spinal cord, and nerves — the body's complete control and coordination network. Its basic unit is the neuron (nerve cell), which is specialised to receive, process, and transmit electrical signals called nerve impulses.
A neuron has three main parts: the cell body (contains nucleus, processes signals), dendrites (short branched extensions that receive incoming impulses), and the axon (single long fibre that carries the impulse away) ending in axon terminals (which transmit the impulse to the next cell at a synapse).
A nerve impulse always travels in one direction within a neuron: Dendrites → Cell Body → Axon → Axon Terminals. At the axon terminal, the electrical signal triggers the release of chemical neurotransmitters across the synapse to the next cell.
Nervous tissue and muscular tissue are interdependent — muscles cannot contract without nerve signals. The brain signals the heart to beat faster during exercise, and all voluntary movement is initiated by motor neurons acting on skeletal muscle via tendons and bones.
Related Concepts from Chapter 2 (Cell: The Building Block of Life)
Nervous tissue is made of neurons — highly specialised cells whose unique structure enables rapid electrical signalling. Review these Chapter 2 pages to understand the cell-level basis of nervous tissue:
Cell: The Building Block of Life — Chapter 2 pillar page; neurons are cells, and every feature of their structure (large nucleus, abundant mitochondria, long axon) reflects specialisation at the cellular level
Cell Organelles — neurons are rich in mitochondria (to fuel continuous electrical signalling), rough endoplasmic reticulum (Nissl bodies, for protein synthesis), and a large nucleus controlling the entire length of a very long cell
Cell Membrane — the nerve impulse is an electrical event generated by the movement of ions (Na⁺, K⁺) across the neuron cell membrane; understanding the selectively permeable membrane from Chapter 2 is essential to understanding how impulses are generated and propagated
Cell — Basic Unit of Life — the neuron is the most dramatic example of how a single cell can be structurally specialised to perform a highly specific function — in this case, transmitting information at high speed across the entire body
